The paper industry has been practicing wastepaper recycling to regenerate usable cellulosic fiber for paper making for many decades. In these processes, ink is removed from the wastepaper pulp using a suitable deinking composition. The deinking process produces a new paper or paperboard product out of materials that might otherwise have ended up in a landfill.
Because of increasing public demand, the use of recycled paper has steadily increased. To recover the fibers used for papermaking from wastepaper, a waste paper deinking operation must generally be carried out to remove the inks used in printing, and thus create suitable characteristics for re-use. Increasing amounts of wastepaper, e.g. old newspapers (ONP) and waste magazines (WM), are becoming available with increased participation of end consumers in recycling.
In the course of conventional paper reclamation, deinking procedures include steps for converting the wastepaper to pulp and contacting the pulp with an alkaline aqueous deinking medium containing a chemical deinking agent. The mechanical action and the alkalinity of the aqueous medium cause the partial removal of ink from the pulp fiber. The deinking agent completes this removal and produces an aqueous suspension and/or dispersion of the ink particles. The resulting mixture is subsequently treated to separate the suspended/dispersed ink from the pulp. This separation may be by flotation and/or washing techniques known in the art.
Conventional deinking chemicals comprise a complex mixture of chemicals, e.g. sodium hydroxide, sodium silicate, chelating agents, hydrogen peroxide, surfactants, dispersants, collector chemicals and agglomeration chemicals. In general, it is standard in deinking to include a significant amount of alkaline material, since it is believed that the alkaline material is needed for sufficient saponification and hydrolysis of the ink resins. In addition, mention is made of the fiber swelling by the caustic being partially responsible for the detachment of ink particles from the fiber surface. Typically, the pH during such a deinking process is from about 9.5 to about 11. Exposing the cellulosic and lignocellulosic fibers to this degree of alkalinity tends to cause yellowing of the fibers and, therefore, it is generally necessary to add an oxidative or reductive bleaching agent, such as peroxide or sodium hydrosulfite. The reductive bleaching step is commonly employed at the end of the deinking process while hydrogen peroxide is added at the pulper. In some deinking operations hydrogen peroxide will be added later in the process.
Furthermore, the alkaline method causes irreversible changes to the pulp fibers, and hence represents a cost to the facility in addition to just the cost of using the chemical. Using caustic will also solubilize papermaking additives and coatings that will lead to additional runnability problems due to deposits at the paper machine.
Thus, there is a need for a deinking process that avoids these shortcomings, which is safe and which is economically and environmentally desirable.
It has been found by the present inventors that treatment of a wastepaper containing pulp with an ink removing system in accordance with the present invention fulfills the above-mentioned requirements to such a deinking process.